Hospital volume, calendar age, and short term outcomes in patients undergoing repair of abdominal aortic aneurysms: the Ontario experience, 1988-92

OBJECTIVE

To determine, for abdominal aortic aneurysm surgery, whether a previously reported relationship between hospital case volume and mortality rate was observed in Ontario hospitals and to assess the potential impact of age on the mortality rate for elective surgery.

DESIGN

Population based observational study using administrative data.

SETTING

All Ontario hospitals where repair of abdominal aortic aneurysm as a primary procedure was performed during 1988-92.

PATIENTS

These comprised 5492 patients with unruptured abdominal aortic aneurysms and 1203 patients with ruptured abdominal aortic aneurysms admitted to hospital between 1988-92 for repair of abdominal aortic aneurysm as a primary procedure.

MAIN OUTCOMES

In-hospital death and length of in-hospital stay.

RESULTS

The case fatality rate was 3.8% for unruptured abdominal aortic aneurysms and 40.0% for ruptured abdominal aortic aneurysms. For unruptured cases, after adjustment for patient and hospital covariates, each 10 case per year increase in hospital volume was related to a 6% reduction in relative odds of death (odds ratio (OR) 0.94, 95% confidence intervals 0.88, 0.99) and 0.29 days reduction (95% CI -0.22, -0.35) in postoperative in-hospital stay. Female sex (OR 1.53, 95% CI 1.08, 2.18) and transfer from another acute care hospital (OR 4.37, 95% CI 2.62, 7.29) were associated with increased case fatality rates among patients in the unruptured category. For ruptured cases, neither the case fatality rate nor postoperative in-hospital stay were significantly related to hospital volume. The case fatality rates increased linearly and substantially with advancing age both for unruptured and ruptured aneurysms, and the excess risk of postoperative death in ruptured as compared to unruptured aneurysms was substantially higher in older patients.

CONCLUSION

The relationship between hospital volume and mortality or morbidity was very modest and observed only for elective surgery. Case fatality rates in patients with ruptured abdominal aortic aneurysms remained 10 times higher than for patients with unruptured abdominal aortic aneurysms, despite improvements in overall mortality in comparison to previously published data. More effective detection of aneurysms, including elective repair for those once considered "high risk" older patients, might further reduce the toll from ruptured aortic aneurysms.

Selective screening for abdominal aortic aneurysm

Abdominal aortic aneurysm (AAA) meets the criteria as a possible target for early detection by screening or case-finding, although the effectiveness of such an intervention has not yet been demonstrated. The purpose of this study was to estimate the increase in cost-effectiveness that would result from selectively screening individuals based on their risk of AAA. Data from a hospital-based case-control study involving 78 men with AAA (unruptured) and 99 male controls were used to derive a risk function based on age, cigarette smoking, high blood pressure, history of heart disease, body mass index and serum high-density lipoprotein, using logistic regression analysis. For each of the control subjects (assumed to be a representative sample of the general population of elderly men), the risk of AAA was estimated and multiplied by the expectation of life to give a measure of the potential benefit of screening. The proportion of the total potential benefit that would be obtained by screening only those with a given level of risk was estimated, and this was related to the proportion of the population screened. In order to obtain 80% of the total potential benefit among men, we found that it would be necessary to examine 52% of the elderly male population if using a risk function based on age alone; 35% would have to be screened if age and smoking were included; and 17% would require screening if all the risk factors were included. Selective screening for AAA appears to be a promising strategy, but a prospective study is required to demonstrate that the predictions are valid.

Trends and variations in the use of vascular surgery in Ontario

OBJECTIVE

To measure changes over time in overall surgical rates and geographic rate variations for three major vascular procedures (abdominal aortic aneurysm repairs, peripheral vascular disease procedures and carotid endarterectomies).

BACKGROUND

There is little research literature on population-based usage profiles of vascular procedures. The three procedures profiled were all subject to marked shifts in evidence or surgical opinions, raising the issue of the interplay between temporal trends and geographic variations in their use.

METHODS

Based on Ontario's hospital discharge abstracts and census data, population-based usage rates were calculated by site of patient residence from 1981 to 1991. Extent of rate variation was summarized with the coefficient of variation, systematic component of variation and the adjusted-likelihood ratio chi2. Spearman rank correlations were also calculated to assess stability of county rankings for each procedure.

RESULTS

The overall rates of peripheral vascular procedures and repair for abdominal aortic aneurysms fell 24% and increased 42% respectively. The overall rate of carotid endarterectomies dropped from 46/100,000 in 1981 to 20/100,000 in 1989, but by 1991 had increased to 37/100,000. Through the decade measures of variation fell minimally for all three procedures.

CONCLUSION

Overall use of vascular procedures shifted in apparent response to new research evidence and technologies. Despite marked changes in surgical rates, the extent of geographic variation was stable, suggesting that differing factors influence overall surgical rates and geographic rate variations. Audit at the local level using primary clinical data is needed to understand why disparities in use persist.

Mesenteric arterial bypass grafts: early and late results and suggested surgical approach for chronic and acute mesenteric ischemia

BACKGROUND

The purposes of this study were to determine the early and late results of placement of arterial bypass grafts in the treatment of chronic and acute intestinal ischemia and to ascertain whether multiple grafts provide better late results than a single graft.

METHODS

Records of 34 patients who underwent mesenteric vascular graft placement were retrospectively reviewed.

RESULTS

All 21 patients with chronic ischemia had a history of intestinal angina and weight loss. Food fear was reported by 33% of patients; also, diarrhea in 57%, constipation in 29%, acalculous cholecystitis in 19%, ischemic gastritis or peptic ulcer in 19%, and elevation of liver enzymes in 22% were reported. Angiogram showed more than 50% stenosis or occlusion of the superior mesenteric artery (SMA) in 100% of patients, celiac artery in 90%, and inferior mesenteric artery in 90%. Although not described previously, a reduction in collateral flow from the internal iliac arteries was caused by severe pelvic disease in 56% of patients. There were no in-hospital deaths. The rate of survival at 1 year was 100%; at 2 years it was 93% +/- 6%, at 3 years 86% +/- 9%, at 5 years 79% +/- 11%, and at 10 years 50% +/- 15%. During follow-up, graft thrombosis occurred in three patients. Of the patients who underwent only a single SMA or celiac bypass, two of five died of bowel infarction; only one of 16 patients who underwent both celiac and SMA bypass had to undergo a repeat surgical procedure because of graft occlusion. Three of 16 retrograde bypasses thrombosed, compared with zero of five prograde bypasses. In nine patients who underwent placement of mesenteric bypass grafts because of acute ischemia caused by acute mesenteric thrombosis, the early mortality rate was 22%; the two deaths were the result of bowel ischemia. The cumulative survival rate was 78% +/- 14% at 1 month, 65% +/- 17% at 1 year, and 52% +/- 16% at 5 years. One of the two late deaths was due to graft thrombosis and bowel infarction. Three of four patients who underwent concomitant mesenteric bypass at the time of aneurysm repair or aortobifemoral bypass survived the surgical procedure.

CONCLUSIONS

When chronic and acute mesenteric ischemia are diagnosed and treated with a bypass graft, the early and late results are good. Complete revascularization of the SMA and celiac artery or pelvis or both and prograde bypass may reduce the risk of late bowel ischemia.

Influence of sex on the results of abdominal aortic aneurysm repair. Canadian Society for Vascular Surgery Aneurysm Study Group

PURPOSE

The purpose of this study is to determine the effect of sex on the survival rate and complications after repair of nonruptured and ruptured abdominal aortic aneurysms (AAA).

METHODS

The Canadian Society for Vascular Surgery Aneurysm Registry formed the database for analysis and provided current, ongoing follow-up of the patients. Statistical methods included t tests, chi-squared analysis, Kaplan-Meier analysis, and Cox regression analysis.

RESULTS

Of the 679 patients undergoing repair of a nonruptured AAA, 19.7% were women and 82.3% men. The following risk factors were significantly different (p < 0.05) in women and men: women were older; more had never smoked; more had a positive family history of AAA; fewer had an electrocardiogram showing evidence of an old myocardial infarction; more had coexisting aortoiliac occlusive disease; fewer had popliteal or femoral aneurysms; and the average size of the AAA was smaller. In spite of potential differences in risk, the in-hospital mortality rates were not affected by sex: 5.2% mortality rate for women and 4.4% for men. Early and late vascular complications occurred with a similar prevalence. The late survival rates were not different in women and men: for women, the 1-, 3-, and 5-year cumulative survival rates were 93.0%, 74.2%, and 63.3%, respectively, and for men 90.3%, 82.8%, and 68.9%. To control for the potential effects of other confounding variables on survival, the Cox proportional hazards method was used. When sex was included in a model along with other significant predictive variables of late survival, sex was not found to be a significant predictor of late results. Of the 146 patients with a ruptured AAA, 13.7% were women and 83.3% men. The in-hospital mortality rates were not significantly different: 55.0% for women and 49.2% for men. There was no difference between the cumulative survival rates: the 3- and 5-year survival rates for women were 36.0% and 9.0%, respectively, and for men 33.9% and 26.9%.

CONCLUSIONS

Sex was not found to have an effect on the early or late results after repair of nonruptured or ruptured AAA. However, a literature review suggests the possibility of a gender bias in the diagnosis and/or selection of patients for surgical treatment because the proportion of women in surgical series is generally less than the proportion determined from autopsy studies, ultrasound studies, hospital discharge data, and national mortality information.

Principles and design feasibility of a Doppler ultrasound intravascular volumetric flowmeter

A new Doppler ultrasound intravascular method is described for the measurement of volumetric flow. Based on the principles described by Hottinger and Meindl [15], it uses a novel semispherical transducer mounted at the tip of a catheter, which generates sample volumes in the form of a thin semispherical shell. Volumetric flow is calculated by using the average velocity determined from the received Doppler spectrum and the area of intersection of a sample volume that completely intersects flow across the vessel. Although a catheter-size transducer was not developed, a larger version was tested using an in vitro steady flow model. Maximum average flow error was limited to 9% for steady flows of 2 to 7 L/min. This error is believed to be a result of the nonuniform intensity generated by the prototype transducer, as well as slight variations in the received power, rather than any fundamental limitations of the flow measurement method itself. Since this study has verified the design principles and feasibility of this new approach, we believe that more detailed experimental investigations are warranted.

Reversal of delayed-onset paraplegia after thoracic aortic surgery with cerebrospinal fluid drainage

We report two patients who had postoperative reversal of delayed-onset paraplegia after cerebrospinal fluid (CSF) drainage after type I thoracoabdominal aneurysm repair. CSF drainage was not initiated before operation because of the urgent presentation of both patients. Decompression of the spinal canal by CSF drainage may improve spinal cord circulation in certain patients and may avoid or decrease neurologic injury. In view of the low morbidity of this intervention, we recommend routine CSF drainage during elective repair of thoracic and thoracoabdominal aneurysms.

Nonruptured abdominal aortic aneurysm: six-year follow-up results from the multicenter prospective Canadian aneurysm study. Canadian Society for Vascular Surgery Aneurysm Study Group

PURPOSE

Based on the prospective analysis of data on 680 patients undergoing surgery for nonruptured abdominal aortic aneurysm (AAA) and recorded in the Canadian Society for Vascular Surgery Aneurysm Registry, this study determines the late survival rate by comparison to an age- and sex-matched population, the causes of late death, the effect of heart-related death on late survival, and the prognostic variables that are associated with late survival.

METHODS

To identify the variables that were associated with survival, statistical methods included Kaplan-Meier analysis and Cox regression analysis. The Canadian Society for Vascular Surgery Aneurysm Registry provided ongoing current follow-up of patients.

RESULTS

The survival rate was 94.6% at 1 month, 90.7% at 1 year, 87.1% at 2 years, 81.0% at 3 years, 74.0% at 4 years, 67.7% at 5 years, and 60.2% at 6 years. The late survival rate of patients with AAA is significantly less than the age- and sex-matched normal population (60.2% versus 79.2%). In the AAA group, heart-related causes of late death (44.4% versus 34.1%) and cerebrovascular causes (8.3% versus 5.8%) were more frequent. The calculated 5-year heart-related mortality rate is 14.3%. This is higher than the heart-related mortality rate for the age- and sex-matched population, which is 6.4%. Hence, the risk of heart-related death for patients who have undergone AAA repair is increased by 1.6% per year. Vascular complications from aortic aneurysm repair or recurrent aneurysmal disease were an uncommon cause of late death: ruptured thoracic aneurysm, 1.5%; ruptured aortic false aneurysm, 1.5%; and aortoenteric fistula, 0%. This incidence appears to be less than reported in earlier series. By Cox regression analysis, the variables that were significant predictors of a lower late survival rate were increased age, preoperative electrocardiogram indicating a previous myocardial infarction, and elevated serum creatinine levels.

CONCLUSIONS

Because cardiac complications accounted for 68.8% (22/32) of the 4.7% in-hospital mortality rate (i.e., a heart-related mortality rate of 3.2%), it seems reasonable to develop a strategy to reduce the cardiac operative risk by identifying and treating patients at high risk before operation. However, it is doubtful that a preoperative program that screens and treats all patients can be cost-effective in preventing late heart-related deaths.

Preoperative factors that predict hospital length of stay after distal arterial bypass

PURPOSE

The purpose of this study was to identify the preoperative factors that are predictive of prolonged hospital length of stay (LOS) and to discuss strategies that might assist in minimizing LOS for this select group of patients.

METHODS

Two hundred seventy-five arterial bypass procedures with the in situ technique were performed between 1986 and 1993. The relationship between 14 preoperative variables and hospital LOS was analyzed with both univariate (Kaplan-Meier) and multivariate (Cox regression) statistical techniques. A model was developed to determine the significant preoperative variables that were associated with prolonged LOS.

RESULTS

The primary and secondary patency rates and limb salvage rates at 4 years were 73.3% +/- 3.2%, 78.9% +/- 2.9%, and 81.9% +/- 3.2%, respectively. The median postoperative LOS was 15 days, with a mean +/- SD of 17.8 +/- 12.3 days (range 4 to 93 days). With Cox regression analysis, the variables that were significant predictors of LOS (with a model p value < 0.002) were age (greater than 74 years vs less than 75), history of cerebrovascular disease (transient ischemic attack, stroke, past carotid endarterectomy vs nil), and operative indication (limb salvage vs disabling claudication).

CONCLUSIONS

This study illustrates that certain preoperative variables are predictive of prolonged postoperative LOS after in situ bypass. The significant preoperative factors identified should be used to direct specific care and discharge planning for these individuals.

Influence of angle on wall shear stress distribution for an end-to-side anastomosis

PURPOSE

The purpose of this article was to study the effects of anastomotic angle on the wall shear stress distribution for end-to-side anastomosis models under pulsatile flow conditions.

METHOD

The photochromic tracer technique was used to visualize the flow field and to determine the instantaneous wall shear stress at multiple locations simultaneously. Models with angles of 20, 30, 45, and 60 degrees were examined.

RESULTS

For all angles, low shear stress was present at the heel and on the bed opposite the heel of the anastomosis apparently as a result of the complete occlusion of the proximal end of the host vessel. Near the toe, increased flow separation occurred with increasing angle. On the bed across from the toe, increasing the angle led to increased shear stress. In addition, in this region the anastomotic angle significantly altered other properties of the shear stress field such as the mean and peak-to-peak magnitudes and cycle-to-cycle fluctuations.

CONCLUSIONS

This study provides quantitative data on the wall shear stress distribution within an end-to-side anastomosis and its relation to the anastomotic angle. The results are discussed in terms of possible roles of shear-induced intimal hyperplasia.

Ruptured abdominal aortic aneurysm: six-year follow-up results of a multicenter prospective study. Canadian Society for Vascular Surgery Aneurysm Study Group

PURPOSE

On the basis of a prospective analysis of 147 patients undergoing surgery for ruptured abdominal aortic aneurysm (AAA) and recorded in the Canadian Society for Vascular Surgery Aneurysm Registry, this study defines the early and 6-year actuarial survival rates and determines the predictive variables that are associated with survival.

METHODS

Ongoing follow-up of a cohort of patients was current at the time of analysis. To identify the preoperative, intraoperative, and postoperative variables that were associated with survival, statistical methods included chi-squared analysis, logistic regression analysis, Kaplan-Meier analysis, and Cox regression analysis.

RESULTS

The survival rate was 48.6% at 1 month, 34.7% +/- 4.2% at 3 years, and 22.0% +/- 4.0% at 6 years. When preoperative and intraoperative variables were considered and logistic regression analysis was used, the highest probability of early in-hospital survival was associated with preoperative creatinine levels of 1.3 mg/dl or less, intraoperative urine output of 200 ml or greater, and infrarenal clamp site. The highest probability of late survival, as calculated by the Cox proportional hazards method, was predicted by the patient's age and total urine output during the procedure. When all variables, including postoperative complications, were considered, late survival was highest if intraoperative urine output was 200 ml or greater and respiratory failure and myocardial infarction did not occur. For those patients with ruptured AAA who survived operation (i.e., greater than 1 month), the long-term survival rate was significantly lower than a comparable group undergoing repair of nonruptured AAA.

CONCLUSIONS

Patients who survive repair of a ruptured AAA have a lower late survival rate than patients undergoing elective repair. When a patient is evaluated before operation, no combination of preoperative variables could identify those patients with little or no chance of survival; hence, the decision to repair a ruptured AAA should be made on clinical grounds. However, after surgery (when information on intraoperative and postoperative variables is also available), the results of this study provide a basis for the surgeon to use these prognostic variables to assist clinical judgment and guide discussions on prognosis with the family and to identify those patients who have such a low chance of early and late survival that further aggressive treatment may be futile.

Flow imaging in an end-to-side anastomosis model using two-dimensional velocity vectors

Colour flow Doppler ultrasound images from vessels of complex geometry can be difficult to interpret, thereby limiting the effectiveness of the technique to correctly assess abnormalities and to relate the images to the underlying flow field in a quantitative manner. This paper describes progress in calculating and displaying two-dimensional (2-D) velocity vectors from a 30 degrees end-to-side anastomosis model under steady flow conditions at various Reynolds numbers. Velocity vectors were computed from colour Doppler ultrasound images obtained with a linear array for several incident beam directions, and the results were displayed either as colour-encoded magnitude images or by superimposing the vectors on one of the original colour images. Results are discussed in relation to flow visualization observations and the behaviour of flow in curved vessels.

Two-dimensional velocity reconstruction strategies for color flow Doppler ultrasound images

A method for calculating the two-dimensional (2-D) velocity vector flow field from color flow Doppler ultrasound images obtained from two or three steering angles has been recently demonstrated. Various strategies for calculating 2-D vectors from noise-corrupted images obtained at multiple angles are described and compared in the present work. This was achieved by using some simple computer flow simulation models to generate color flow images for various beam steering angles. Velocity vectors were calculated for the entire image, and the vectors are displayed at selected points by superimposing them on a magnitude image. It is shown that such displays help improve the qualitative understanding of images obtained from vessels with complex flow geometry. The bias and variance of four reconstruction methods are compared for stimulated laminar flow in a tube. Based on the simulation results, it was found that the dominant factor that affects the reconstruction accuracy is the angle between the observation directions, and that a simple two component method generally gives as good a performance as the more complex alternatives that were studied.

Thrombosis of the axillary artery secondary to compression by the pectoralis minor muscle

This case presentation reports the second case of axillary artery thrombosis secondary to pectoralis minor compression. Evidence to explain this etiology is presented from arteriographic and intraoperative clinical findings. Management includes division of the pectoralis minor muscle and local arterial repair if the vessel is severely damaged.

Hemodynamics of a side-to-end proximal arterial anastomosis model

PURPOSE

The purpose of this article was to analyze the fluid mechanical effects of a side-to-end proximal anastomosis and to compare the results with those from our earlier study on the end-to-side distal anastomosis.

METHODS

The photochromic tracer technique was used to determine the instantaneous wall shear stress and to visualize the overall flow field under pulsatile flow conditions. The flow consisted of a sinusoid plus a steady component with mean and modulation Reynolds numbers of 355 and 565, respectively, and a Womersley number of 7.9.

RESULTS

At the toe and heel of the junction, very high and positive wall shear stresses were seen together with substantial nonperiodic fluctuations. The peak wall shear stress was about four times higher at the toe and about seven times higher at the heel than the maximum values observed at about four tube diameters upstream from the junction. On the bed of the host vessel, nonperiodic fluctuations were also observed, but the shear stresses were mainly negative with magnitudes comparable to those seen upstream. With leakages of 11% and 28% of the mean flow through the blocked end of the host vessel, the shear stress pattern seemed to be significantly affected only at the toe for the higher leakage. Further, when the mean Reynolds number was reduced to 320, the magnitudes of the variations in the wall shear stress were reduced proportionately, except at the heel, where the reduction was much larger than expected.

CONCLUSIONS

It appears that the preferential development of intimal hyperplasia at the distal end-to-side anastomosis may be promoted by low wall shear stress at the toe and heel, and probably by high shear stresses or shear stress gradients on the bed.

Three-dimensional display of calculated velocity profiles for physiological flow waveforms

PURPOSE

To improve the understanding of the nature of pulsatile flow, three-dimensional idealized velocity profiles corresponding to measured physiological mean flow velocity waveforms were displayed at selected instants throughout the flow cycle.

METHODS

The Fourier harmonics for each waveform were determined, and their corresponding velocity profiles at each instant of time were calculated with the Womersley equations. Velocity profiles were calculated by summing the contributions from each harmonic.

RESULTS

Calculated profiles were displayed in a three-dimensional perspective for both normal carotid and femoral arteries and for simple sinusoidal flow with a superimposed steady component.

CONCLUSION

The potential value of such displays is discussed in terms of gaining an improved understanding of the nature of pulsatile flow and clarifying the interpretation of Doppler ultrasound recordings.

A numerical simulation of flow in a two-dimensional end-to-side anastomosis model

In order to understand the possible role that hemodynamic factors may play in the pathogenesis of distal anastomotic intimal hyperplasia, we carried out numerical simulations of the flow field within a two-dimensional 45 degree rigid-walled end-to-side model anastomosis. The numerical code was tested and compared with experimental (photochromic dye tracer) studies using steady and near-sinusoidal waveforms, and agreement was generally very good. Using a normal human superficial femoral artery waveform, numerical simulations indicated elevated instantaneous wall shear stress magnitudes at the toe and heel of the graft-host junction and along the host artery bed. These sites also experienced highly variable wall shear stress behavior over the cardiac cycle, as well as elevated spatial gradients of wall shear stress. These observations provide additional evidence that intimal hyperplasia may be correlated to wall shear stresses over the cardiac cycle, high wall shear stress gradients, or a combination of the three. The limitations of the present work (especially in regard to the two-dimensional nature of the flow simulations) are discussed, and results are compared to previous observations about distal anastomotic intimal hyperplasia.

Iliac arteries: reanalysis of results of balloon angioplasty

In this reanalysis of the 667 percutaneous transluminal balloon angioplasties (PTAs) of the iliac arteries, the variables that are predictive of early and late success were identified. For 82 iliac occlusions, the success rate at 1 month was 75.6% +/- 4.7 (mean +/- standard error). With exclusion of the 15 technical failures that were associated with one complication, the success rate at 1 month was 91.0% +/- 3.5 and at 3 years, 58.8% +/- 7.1. For PTA of an iliac occlusion at one site, the predicted 3-year success rate was 66%, whereas for PTA of an iliac occlusion with a tandem lesion, the success rate was 17%. For the 313 common iliac PTAs, the success rate at 1 month was 97.1% +/- 0.9; at 1 year, 81.1% +/- 2.3; at 2 years, 70.6% +/- 2.9; at 3 years, 67.8% +/- 3.0; at 4 years, 64.9% +/- 3.3; at 5 years, 60.2% +/- 4.0; and at 6 years, 52.0% +/- 5.7. There were no variables that were statistically predictive of late results. For the 209 external iliac PTAs, the predicted 3-year success rate was 57% for men and 34% for women. For 58 PTAs of both common and external iliac stenoses, the predicted 3-year success rate was 73% for patients with good runoff and 30% for those with poor runoff. Serious complications were recorded in 3.9% (26 of 667): Death occurred in 0.3%, operation was necessary in 1.0%, and hospital discharge was delayed in 2.6%.

On the Doppler signal from a steady flow asymmetrical stenosis model: effects of turbulence

A steady flow model with a 70% (by area) asymmetrical stenosis was used to examine how changing flow regimes (laminar to turbulent) affect the Doppler signal. Human red blood cells (RBCs) (Hct = 42%) in saline were employed at a flow rate corresponding to a Reynold's number of approximately 545. A dilute suspension of 4% fixed RBCs was also used for the purpose of backscattered power comparison. Measurements of the Doppler signal enabled the backscattered power, time domain statistics, frequency spectra, frequency domain statistics, various spectral indices, autocorrelation function and decorrelation time to be calculated as a function of distance from the stenosis. It is shown that the characteristics of the Doppler signal measured at each site provide information on the nature of the insonated flow field and these correlate well with those expected. The results demonstrate that the onset of turbulence not only affects the Doppler spectrum but also has a profound effect on the signal power, the decorrelation time and the signal statistics.

Factors that influence the outcome of aortoiliac and femoropopliteal percutaneous transluminal angioplasty

In the past, patients with peripheral arterial occlusive disease were managed by conservative treatment or by vascular reconstructive surgery. Now, percutaneous transluminal angioplasty and other endovascular methods provide an important alternative for managing selected patients with peripheral arterial occlusive disease. Overall, the 5-year success rate after iliac angioplasty is 53.4%, but the success rate is higher if percutaneous transluminal angioplasty is performed on the common iliac artery or on a stenosed artery. In contrast, percutaneous transluminal angioplasty of the femoral and popliteal arteries has a relatively poor long-term success rate except for the treatment of patients with stenoses with good run-off. When the run-off is poor or an arterial occlusion is present, the role of femoropopliteal angioplasty is limited, and the procedure should be considered only for high-risk patients who do not have autogenous tissue for reconstructive surgery.